The invention relates to an apparatus for producing mineral fibres from silicate raw materials such as basalt, in particular by blast drawing.
When blast drawing is used to produce mineral fibres, the mineral fibres emerging from the fiberisation unit in the form of a blast nozzle unit pass into a chute, along the length of which the jet of flow medium which carries the fibres has the opportunity to fan out, so that the fibres fill out the cross-section of the chute in substantially homogeneous manner and thus can be laid onto a conveyor belt to form a mineral fibre web. In the entry zone of the chute, fluid binder such as phenolic resin is sprayed in and adheres to the fibres and descends thereon onto the conveyor belt. In the course of their descent, fibres which are at the edge come into contact with the circumferential walls of the chute, in particular in the lower section of the chute, so that the binder adhering to the fibres can have the effect of causing the fibers to adhere to the walls of the chute. As a consequence of the relatively high temperature in the chute, which is continuously supplied by the fiberisation units with fibres of comparatively high temperature, the result can be that the binder becomes cured on the chute walls and can form encrustations which are afterwards very difficult to remove.
To avoid that it is known to construct at least the side walls of the chute to be movable over a major area, namely as so-called rotary walls, in such a way that the side walls basically constitute upright conveyor tracks whose conveyor belt is in constant motion. The adhering fibres are thus transported with the conveyor belt out of the zone of the chute interior, where the surface of the belt is cleaned and can be guided back into the chute interior on the other side.
In this way it is perfectly possible to remove a large portion of the adhering fibres in a continuous manner in a continuous operation and thus to avoid larger and more stable encrustations.
This known procedure, which corresponds to the conventional technology in the field, however, is extremely costly, not only in terms of investment costs but also in terms of maintenance costs. The drives for the rotary walls are subject to marked contamination and therefore tend to break down. If the unit is stationary for refitting or repair work or the like, no cleaning takes place although it is nonetheless possible for encrustations which are difficult to remove to be formed. Residues which escape the cleaning device, in particular in the interior of the rotary walls, likewise form a virtually unremovable deposit of dirt. When encrustations are in the process of formation or have formed and are subsequently rubbed off, for example through an adjustment of the cross-section of the chute, they end up on the production belt where they cause production errors and interferences within the area of the discharge from the chute.
If merely the large-area side walls and not the front walls of the chute are equipped with such rotary walls, corresponding encrustations on the front walls are unavoidable, and these encrustations can grow to a considerable size until they for example drop off through their own weight and in this way cause production problems.
It has also been found to be a severe problem that it is virtually impossible to produce a dimensionally truly accurate seal between the rotary walls and rigid walls and especially between rotary walls which may be adjacent. As a result, a considerable amount of unwanted air passes into the chute and needs to be evacuated underneath the conveyor belt together with the wanted secondary air sucked in by way of the chute. There are also appreciable fibre losses due to the egress of fibre through leaks in the chute, which need to be added to the fibre lost due to encrustations and the like.